Electrode design and positioning for controlled movement of a moveable electrode and associated support structure

ABSTRACT

A MEMS system including a fixed electrode and a suspended moveable electrode that is controllable over a wide range of motion. In traditional systems where an fixed electrode is positioned under the moveable electrode, the range of motion is limited because the support structure supporting the moveable electrode becomes unstable when the moveable electrode moves too close to the fixed electrode. By repositioning the fixed electrode from being directly underneath the moving electrode, a much wider range of controllable motion is achievable. Wide ranges of controllable motion are particularly important in optical switching applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. application Ser. No. 10/136,683 filed Apr.30, 2002 by the same inventors, and claims priority therefrom. Thisdivisional application is being filed in response to a restrictionrequirement in that prior application and contains additional claims tothe restricted subject matter. The contents of the original U.S.application Ser. No. 10/136,683 are hereby incorporated by reference inits entirety.

BACKGROUND

MicroElectroMechanical systems (MEMS) routinely use suspendedmicromechanical moveable electrode structures as electrostaticallyactuated mechanical members for both sensor and actuator based devices.Different methods exist for creating a support structure to suspend amoveable electrode structure. One method for suspending such a moveableelectrode uses cantilevered members that are fixed to a substrate on oneend and fixed to the movable electrode structure on the other end. In analternate embodiment, the cantilever is made of, or coated with aconducting material and the cantilever itself serves as the movingelectrode. The mechanical flexibility of the cantilever (e.g. bending)and/or motion at the fixed end(s) (e.g. hinge or flexible connection)allows for the motion of the suspended electrode. In some cases, thesensor or actuator device is based on motion of cantilever as suchwithout an additional movable structure at the end of the cantilever.Such cantilevers are typically fixed-free or fixed-simply supportedcantilevers.

A second method of suspending one or more moveable electrodes utilizes aplurality of cantilevers that support a moveable member which eitherserves as a moveable electrode or has mounted upon it moveableelectrodes. A fixed electrode serves as an actuator to control movementof the moveable electrode structure through the application of anelectric potential difference between the fixed electrode and themoveable electrode structure. The fixed electrode is typicallypositioned beneath the suspended moveable electrode to form a parallelplate capacitor like structure, with the fixed electrode acting as afirst plate and the suspended moveable electrode acting as a secondplate. The electric potential applied to the electrodes generateselectrostatic forces that move or deform the support mechanismsupporting the moveable electrode or the moveable electrode itself. Suchsupport mechanisms may include bendable or otherwise deformablecantilevers.

Typical cantilever applications include micro sized relays, antennas,force sensors, pressure sensors, acceleration sensors and electricalprobes. Recently, considerable attention has been focused on usingcantilever arrays to develop low power, finely tunable micro-mirrorarrays to redirect light in optical switching applications. Such astructure is described in U.S. Pat. No. 6,300,665 B1 entitled “Structurefor an Optical Switch on a Silicon on Insulator Substrate” herebyincorporated by reference.

One problem with such cantilever structures is the limited amount ofcontrollable motion that can be achieved with traditional arrangementsof the cantilever and electrode. When a voltage difference is appliedbetween two electrically conducting bodies separated by an insulatingmedium (for example air), the electrostatic force between the two bodiesis inversely proportional to the square of the distance between thebodies. Thus when the moveable electrode is moved in closer proximity tothe fixed electrode, as often occurs when a greater range of motion isattempted, strong electrostatic forces between the fixed electrode andthe moveable electrode results in a “pull-in” or “snap-down” effect thatcauses the two electrodes to contact. The problem is particularly acutein D.C. (direct current) systems compared to A.C. (alternating current)systems.

In moving the electrodes, instability theoretically occurs in parallelplate capacitor structures when the movably suspended plate has traveledone third of the potential range of motion (typ. equal to the height ofthe air gap). In stressed metal systems, as described in the previouslycited patent application, the cantilevers are typically ‘curled’—asopposed to more typical ‘straight’ cantilevers. However, suchinstability usually occurs when the actuation electrode is placedunderneath the cantilever and the cantilever moves approximately beyondone-third of its potential range of motion.

Various solutions have been proposed to correct the potential forsuspended electrodes and the corresponding supports structures to“snap-down”. These solutions include the following: using charge drives(see Seeger, et. al, “Dynamics and control of parallel-plate actuatorsbeyond the electrostatic instability”, Proc. Transducers '99, Sendai),adding capacitive elements in series (Seeger, et. al, “Stabilization ofElectrostatically Actuated Mechanical Devices”, Proc. Transducers '97,Chicago) or creating closed-loop feedback systems using capacitive,piezoresistive or optical detectors (Fujita “MEMS: Application toOptical Communication”, Proc. of SPIE, '01, San Francisco). Thesemethods extend the stable range of motion to varying degrees. Howeverall these methods complicate fabrication of the cantilever and actuatormechanism thereby increasing fabrication costs and reducing reliability.Thus an improved method of moving a cantilever through a wide range ofmotion while avoiding instabilities is needed.

SUMMARY OF THE INVENTION

An improved system for controlling electrostatic deflection of a supportmechanism associated with a moving electrode is described. In thesystem, a fixed electrode formed on a substrate uses electrostaticforces to control the motion of a moveable electrode coupled to asupport structure. In order to avoid the strong electrostaticattractions that occur when the moveable electrode comes in closeproximity to the fixed electrode on the substrate, the electrodes areoffset such that a substantial portion of the fixed electrode isadjacent to, rather than directly in the path of the moveableelectrode's range of motion.

BRIEF SUMMARY OF THE DRAWINGS

FIG. 1 shows a side view of a moveable electrode and a fixed electrode.

FIG. 2 shows a side and top view of a second support structure used tosuspend a moveable electrode over a fixed electrode.

FIG. 3 is a flow chart showing one example method of forming acantilever in a MEMS structure.

FIG. 4 shows a top view of a traditional placement of electrodes withrespect to the cantilever.

FIG. 5 shows a top view of one possible placement of rectangularelectrodes with respect to the cantilever.

FIG. 6 shows a top view of one possible placement of triangularelectrodes with respect to the cantilever.

FIG. 7 shows a top view of a possible placement of a triangular orrectangular electrode with respect to a cantilever with a cutout area.

FIG. 8 is a graph showing a theoretical plot of cantilever height withrespect to applied voltage for various electrode and cantileverstructures.

FIG. 9 shows a cantilever used in a optical switching system.

FIG. 10 shows a plurality of cantilevers coupled to a mirror to redirectan optical beam across a two dimensional area.

DETAILED DESCRIPTION

FIGS. 1 and 2 show two examples of MEMS cantilevered actuatorstructures. FIG. 1 shows a side view of a simple fixed end—free endcantilever-electrode structure. The example of the cantilever shown inFIG. 1 is a flexible cantilever that flexes upward and may be formedusing techniques for forming stressy metal structures as described inU.S. Pat. No. 5,613,861 entitled “Photolithographically Patterned SpringContact” which is hereby incorporated by reference. In FIG. 1, aflexible cantilever 104 is affixed to a substrate 108 at a fixed point112. Typically, the cantilever is composed of or coated with anelectrically conducting material to form a suspended moveable electrode114 that facilitates the generation of electrostatic forces betweenmoveable electrode 114 and a fixed electrode actuator. Examples ofsuitable materials for forming the cantilever include metal, silicon andpolysilicon. In an alternate embodiment, the cantilever is a stressedmetal to create the curve structure illustrated. Such stressy metalcantilevers may be formed from a refractory metal such as molybdenum,zirconium and/or tungsten (Mo, Zr, W).

Fixed electrode 116 deposited on substrate 108 controls movement ofmoveable electrode 114 and thereby cantilever 104. Moving electrode 114moves in an arc in a motion plane 110, which in the illustrated example,is oriented perpendicular to the substrate surface (in the illustratedembodiment, the paper in which the drawing is drawn represents motionplane 110). When a voltage difference is applied between fixed electrode116 and moving electrode 114, cantilever 104 moves towards fixedelectrode 116. When moving electrode 114 is maximally displaced along atrajectory of motion in motion plane 110 such that moving electrode 114is in the lateral plane of substrate 108, the position of the movingelectrode is shown by outline 120. In FIG. 1, cantilever 104 flexesalthough in an alternate embodiment, a rigid cantilever may pivot aroundfixed point 112.

Cantilever 104 may be made of a variety of materials such as metal,silicon, polysilicon or other electrically conductive materials to serveas a moveable electrode. Alternatively, the cantilever may be made of aninsulating material such as polymers, ceramics and the like, andsubsequently coated with a conductive material such as a metal film, theconductive material coating serving as the moveable electrode.Appropriate dimensions of the cantilever are a length 118 of less than5000 micrometers (less than 500 typical) and a width of less than 1000micrometers (less than 100 typical) although alternate embodiments mayuse larger cantilevers.

In order to maintain control over the moving electrode and itsassociated support structure through a large range of motion, the fixedelectrode is positioned such that it is laterally adjacent to, ratherthan directly underneath the cantilever. For purposes of discussion,“laterally adjacent” is defined as a position adjacent to the trajectoryof the moving electrode such that even when the moving electrode ismaximally displaced such that the moving electrode, in this case thecantilever, is in the lateral plane of the substrate, the two electrodesare adjacent in the plane of the substrate. In most cases, even when themoving electrode moves in an arc, the arc radiuses are small such thatthe moving in a trajectory is practically equivalent to translating thesuspended electrode along a line perpendicular to the surface of thesubstrate supporting the fixed electrode. Once the two electrodes are inthe plane of the substrate, “laterally adjacent” does not require orimply that the moving electrode and the fixed electrode are in contact,merely that the electrodes are close, typically separated by less thanapproximately 50 micrometers (e.g. 5 μm) when the moving electrode is inthe lateral plane of the substrate. It is contemplated however, that thesystem may still operate when the electrodes are not entirely laterallyadjacent, thus when small amounts of overlap result, typically less than10 percent of the electrode surface are, fringe electric fields are thedominant source of attraction between the moving electrode and the fixedelectrode and stability may still be archived.

Even when the cantilever is not displaced from its resting position, thedistance from the fixed electrode to the moving electrode should be keptrelatively small, for example less than 10 micrometers to allow theeffects of electrostatic attraction to control movement of thecantilever in a reasonable voltage range (typically less than 200volts). When the entire surface area of the electrode is laterallyadjacent to rather than underneath the cantilever; direct contactbetween the cantilever and the electrode when the cantilever is at amaximum displacement is avoided thereby making an insulating layer overthe fixed electrode unnecessary.

A side view of an alternative mechanism for suspending a movingelectrode is shown in FIG. 2. The structure of FIG. 2 is a slightvariation on what is typically called a Lucent mirror, Lucent mirrorshave traditionally been used to redirect light in optical systems. InFIG. 2, a straight, torsionally flexible cantilever 204 is affixed to asubstrate 208 at a fixed point 212 and affixed to a movably suspendedmember 216. Together, the elements represent a support structure for amoving electrode. In one embodiment of the invention, member 216 iscomposed of or coated with an electrically conducting material and thusalso serves as the moveable electrode. The conducting material aids thegeneration of electrostatic forces between the moveable electrode and afixed electrode 220 that serves as an electrode actuator. Examples ofsuitable materials from which to form the moveably suspended memberinclude metal, silicon and polysilicon. Fixed Electrode 220 on substrate208 controls movement of member 216. In the illustrated embodiment,member 216 rotates about an axis 224. Axis 224 is oriented parallel withthe substrate surface. When a voltage difference is applied betweenfixed electrode 220 and a moving electrode associated with member 216,member 216 rotates towards the fixed electrode. In the illustratedembodiment, cantilever 204 flexes torsionally although in alternateembodiments the tortional flexing may be replaced by a rigid cantileverthat pivots around fixed point 228.

Flexing cantilever 204 may be made of a variety of flexible materialssuch as metal, silicon, polysilicon. Appropriate dimensions of thecantilever are a length 232 of less than 5000 micrometers (less than 500typical) and a width of less than 1000 micrometers (less than 100typical) although alternate embodiments may use larger cantilevers. Inorder to maintain control over movements through a large range ofmotion, the fixed electrode is positioned such that it is laterallyadjacent to, rather than directly underneath the moving electrode, inthe illustrated example, suspended member 216 is formed from aconducting material and serves as the moving electrode. Even when thesuspended member is not displaced from its resting position, thedistance to the fixed electrode should be kept relatively small, forexample less than 10-100 micrometers to allow the effects ofelectrostatic attraction to control movement of the cantilever in areasonable voltage range (typically less than 200 volts). When theentire surface area of the electrode is laterally adjacent to ratherthan underneath the suspended member; direct contact between thecantilever and the electrode when the cantilever is at a maximumdisplacement is avoided thereby making an insulating layer over eitherelectrode unnecessary.

In yet another variation of the structure shown in FIG. 2, voltagedifferences may be simultaneously applied between suspended member 216and multiple fixed electrodes such as fixed electrode 220, therebycausing suspended member 105′ to translate downward, towards the planeof the fixed electrodes. By keeping the forces approximately equalacross the suspended member, rotational motion may be avoided. In thistranslational case, instability occurs at one third of the potentialtravel range when fixed electrodes 220 are placed directly underneathsuspended the moving electrode represented by suspended member 216.Laterally offsetting the electrodes as shown in FIG. 2 substantiallyextends the stable range of motion beyond one third of the potentialrange, approaching the full potential travel range.

A number of methods exist to fabricate cantilever and actuator MEMSstructures. FIG. 3 illustrates one method of fabricating the cantileverelectrode structure using a three step semiconductor masking process.Although the process is described to enable one of ordinary skill in theart to fabricate a semiconductor cantilever, the invention should not belimited to the particular type of cantilever described nor theparticular method used to fabricate the cantilever and electrodestructures.

In operation 304 of FIG. 3, an electrode material is deposited on asubstrate such as glass or quartz. The electrode material may be madefrom a number of conducting materials or metals such as chromium. Afterdeposition, a pattern masking and wet etch is done in operation 308 todefine the electrode and tracks or wires that couple the electrode tocontrolling circuitry. The controlling circuitry controls the charge anddischarge of the electrode thereby controlling the motion of thecantilever. The thickness of the electrode may be tuned to obtain asheet resistance suitable for resistive sensing. Chromium has aresistivity of about 130×109 Ohms/M, thus a thin film of 25 nm resultsin about 5 ohms/square.

In operation 312, a release layer, such as an amorphous silicon releaselayer is deposited. Typically, the release layer thickness determinesthe spacing between the cantilever and the substrate surface. Therelease layer is often slightly thicker than the electrode layer. Therelease layer serves as a buffer layer to prevent the entire subsequentcantilever layer from adhering to the substrate. A cantilever layer,such as a Molybdenum chromium (MoCr) layer is deposited in a blanketcoat over the release layer in operation 316. A typical cantileverthickness is approximately 1 micrometer. When a stressed metalcantilever is desired, a stressed metal deposition is used to depositthe cantilever layer.

In operation 320, a second mask layer is used to define the cantilevershape by etching away the excess MoCr. In operation 324, the releaselayer is etched to release the cantilever leaving only one end of thecantilever affixed directly to the substrate. A typical method foretching a silicon release layer utilizes a dry etch of XeF2 as theetchant. When using other release layer materials, such as for examplesilicon oxide, a wet etch (e.g hydrofluoric acid) is typically used toremove the sacrificial layer.

FIGS. 4, 5, 6 and 7 are top views of the fixed electrode and a movingelectrode cantilever structure that show alternate positions of theelectrodes with respect to the cantilever. FIG. 4 shows a top view of atraditional cantilever over electrode structure. At contact area 404,the cantilever is fixed to an underlying substrate, either directly orthrough an intermediate layer. The flexing region 408 of the cantileverrests directly over an electrode underneath which controls movement ofthe cantilever. The close proximity and direct application of force byelectrodes positioned underneath the cantilever minimizes theoperational voltage needed to move the cantilever. However, the reducedpower requirements come at the expense of great instability. Voltagesgreater than a critical voltage results in the cantilever “snapping”down towards the substrate.

FIG. 5 shows one embodiment of the invention that utilizes rectangularstrip electrodes 504 oriented with a length that runs parallel to thelength of cantilever 508. Because electrodes 504 are not positioneddirectly underneath the cantilever, the laterally displaced rectangularstrip electrodes depend on fringe electric fields to pull the cantileverdownward. As the cantilever moves downward towards the substrate, theforce vector of the electric field between the cantilever and theelectrode increasingly points in a lateral direction (in the plane ofthe substrate) rather than in a downward direction towards thesubstrate. Thus, although the intensity or absolute value of theelectric field increases as the cantilever moves toward the substrate, agreater percentage of the force is applied in a lateral directionreducing the rapid increase in electric field strength downward. Asymmetrical arrangement of electrodes around the cantilever causes thelateral force components to cancel thereby minimizing displacement ofthe cantilever in a lateral direction.

To further increase the stable range of motion, triangular electrodes604, 608 may be substituted for the rectangular electrodes as shown inFIG. 6. In this embodiment, the distance between the cantilever and thefixed electrodes increases along the length of the cantilever. Theincreasing distance between the cantilever and the fixed electrodefurther reduces the force for a given voltage along the length of thecantilever further increasing the stable range of motion. The embodimentof FIG. 6 requires the highest voltages compared to the structures shownin FIG. 5 and FIG. 6 to achieve an equivalent displacement of thecantilever, although the actual voltage required depends on many factorsincluding cantilever and electrode geometries, dimensions of thecantilever, material properties, etc. A typical voltage to achieve alarge displacement of cantilever 612 may be approximately 150 volts.Because the triangular electrodes also provide a fairly constant balancebetween applied force on the cantilever and cantilever flexibilityacross the length of the cantilever, the configuration illustrated inFIG. 6 provides the most stable configuration.

The triangular electrodes shown in FIG. 6 results in a spacing betweenthe cantilever and the edge of the electrode remaining fairly linearwith respect to voltage applied to the electrodes. In general, stabilityof the system is increased when the moving and/or fixed electrode isshaped such that the distance between the closest point on the fixedelectrode and the closest point on the moving electrode increases withdistance from the point at which the support structure supporting themoving electrode is coupled to the substrate. Various ways ofaccomplishing the gradually increasing distance include formingtriangular fixed electrodes, forming triangular moving electrodes, orangularly orienting rectangular fixed and moving electrodes such thatthe space between the edges of the electrodes form a triangle. Otherembodiments of the invention may also use electrodes with other taperedgeometries (e.g. curved as opposed to straight). These differentconfigurations may be used to linearize or otherwise tailor thedisplacement versus voltage curve.

FIG. 7 shows an embodiment of the invention in which a tapered (orstraight) fixed electrode 704 is formed underneath a cutout area 708 ofcantilever 712. This and other types of ‘cutout’ cantilevers with‘internally adjacent’ electrodes are based on the same concept as otherlaterally offset actuation electrodes, but may offer additionaladvantages. For example, the embodiment shown in FIG. 7 offers theadvantages of adjacent electrodes while utilizing a minimum of area.

FIG. 8 is a graph that shows the vertical height of a cantilever tip inmicro-meters as a function of a direct current (D.C.) voltage applied tothe electrode for different electrode geometries and positions based ona simple numerical model. Each line 804, 808 and 812 can be divided intotwo regions: (1) an actuation region in which an air gap exists betweenthe cantilever and the substrate resulting in a nonzero cantilever tipheight and (2) a critical voltage at which the cantilever “snaps” downto the substrate eliminating the gap between cantilever and substrate.

Line 804 shows the cantilever tip position as a function of electrodevoltage for a traditional positioning of an electrode under thecantilever. In the model, the cantilever can only be controlled at aheight displacement above approximately 110 micrometers. Atapproximately 20 volts, snap-down occurs after which manipulation of thecantilever over small displacements cannot be well controlled. When theelectrode is placed under the cantilever, typically, the entirecantilever snaps down.

Line 808 shows a modeling of the cantilever height as a function ofvoltage for two rectangular parallel electrodes positioned adjacent tothe cantilever as shown in the top view of FIG. 4. From line 808, it canbe observed that the displacement of the cantilever can be wellcontrolled for cantilever heights above 100 micro-meters. The cantileversnaps down at a critical voltage of approximately 55 volts.

Line 812 plots cantilever height as a function of voltage for twoelectrodes positioned laterally adjacent to the cantilever, the twoelectrodes shaped such that the electrode edges closest to thecantilever increases in distance from the cantilever edge as one movesalong the length of the cantilever. Such a structure may be achieved byusing triangular electrodes as was shown in FIG. 6, or by orientingstraight lines electrodes such that they point slightly away from thecantilever edges. Comparing line 812 to lines 804 and 808, it can beseen that the actuation region for the laterally adjacent triangularelectrodes is substantially larger than the actuation region for theelectrode positioned underneath the cantilever and the rectangularelectrodes positioned laterally adjacent to the cantilever. Thus thecantilever has a large actuation region allowing for control of thecantilever over a wide range of voltages and tip heights.

It should be understood that the foregoing described cantilevers may beused for a variety of structures, systems and applications, includingbut not limited to optical switching. FIG. 9 shows a simple cantileverused in a simplified optical switching system. In FIG. 9, an opticalfiber 904 in an array of optical fiber acts as a light source thatoutputs a ray of light 908. The ray 908 is focused by a lens 912 anddirected to a mirror 916. The position of mirror 916 is controlled byelectrode 920 positioned laterally adjacent to cantilever 924. Theorientation of mirror 916 determines which lens in receiving lens array928 receives light. The receiving lens focuses the received light on acorresponding fiber in receiving fiber array 932.

In the illustrated embodiment of FIG. 9, mirror 916 positioned at theend of cantilever 924 offers movement in only one plane along an arcthat represents the motion of a single cantilever. However, in arrayswitching operations, it may be desirable to redirect light to variouspoints in a two dimensional array.

FIG. 10 shows a mirror region 1004 affixed to the end of a plurality ofcantilevers 1008, 1012, 1016, and 1020. Each cantilever, such ascantilever 1008, includes a fixed end, such as fixed end 1024 affixed toan underlying substrate. Fixed electrodes, such as electrodes 1028 andelectrode 1032 typically are formed on the underlying substrate and runalong the perimeter of a corresponding cantilever. Each electrode, suchas electrode 1028 can be considered laterally adjacent to thecorresponding cantilever and may be used to deflect the correspondingcantilever. An end of cantilever 1008 opposite fixed end 1024 is coupledto mirror region 1004, thus as the cantilever moves up or down, the edgeof the mirror coupled to the cantilever also moves up or downaccordingly. The portion of the electrode near the fixed end such asfixed end 1024 serves mainly to couple the different sections of theelectrode and keep the entire electrode at a fixed potential.

Other configurations of cantilevers and mirrors are also available asdescribed in patent application Ser. Nos. 09/672,381 and 09/675,045entitled “Method for an Optical Switch on a Silicon Substrate” and“Structure for an Optical Switch on a Substrate” respectively, bothpatent applications are hereby incorporated by reference. Control of thevarious mirror and cantilever configurations described in the referencescan be improved by placement of electrodes adjacent to the cantilevers.

The foregoing description includes a number of details that are providedto provide a clear understanding of the technology and the invention aswell as to provide examples of different ways of using and/orimplementing the technology. Details in the description such asdimensions, materials used to fabricate the device, and particulargeometries should not be used to limit the invention. Likewise, itshould be appreciated by those skilled in the art that other geometriesand combinations are possible for suspension cantilevers and suspendedstructures, as well as for mechanical motions. It will also beappreciated by those skilled in the art that the presence of laterallyoffset electrodes does not preclude the presence of other, additionalelectrodes in any position or orientation, for any additional purpose(such as linearizing the deflection vs. voltage curve and the like).Thus, the invention should only be limited by the restrictions recitedin the claims which follow.

1. A method of moving a moving electrode using electrostatic forcescomprising: applying a voltage such that a voltage difference is formedbetween a suspended moving electrode and a fixed electrode positionedlaterally adjacent to the moving electrode, the applied voltage causingthe moving electrode to move toward a point on a substrate underneaththe moving electrode, the point adjacent to said fixed electrode.
 2. Themethod of claim 1 wherein each electric field that electrostaticallymoves the moving electrode is a fringe electric field from the fixedelectrode.
 3. The method of claim 1 wherein at least ninety percent ofthe top surface of the fixed electrode extends beyond a surface coveredby the moving electrode when the moving electrode moves into a planeapproximately parallel with the substrate.
 4. A method of moving amoveable electrode comprising the operations of: applying a voltage toat least one electrode to create a difference in electric potentialbetween a moveable electrode and a fixed electrode in a fixed electrodeplane, the fixed electrode positioned laterally adjacent to the moveableelectrode; and, adjusting the difference in electric potential to causemovement of the moveable electrode in a motion plane approximatelyperpendicular to the fixed electrode surface.
 5. The method of claim 4wherein at least ninety percent of the fixed electrode extends beyond asurfaced covered by the moveable electrode when the moveable electrodemoves approximately adjacent the fixed electrode plane
 6. The method ofclaim 4 wherein the moveable electrode is a cantilever.
 7. The method ofclaim 4 wherein the difference in electric potential is between 30 and100 volts.
 8. The method of claim 4 wherein the moveable electrodeincludes a moveable tip, a gradual 75 percent decrease in electrode tipdistance from the fixed electrode plane achievable over several voltschange in the difference in electric potential.
 9. The method of claim 4wherein the moveable electrode in triangular in shape.
 10. The method ofmoving a moveable electrode in a MicroElectroMechanical systemcomprising the operations of: determining a desired position of amoveable electrode; applying a voltage to at least one electrode of amoveable electrode and a fixed electrode to create a difference inelectric potential between the moveable electrode and the fixedelectrode, the fixed electrode in a fixed electrode plane, the fixedelectrode positioned laterally adjacent to the moveable electrode; and,adjusting the difference in electric potential to cause movement of themoveable electrode in a motion plane approximately perpendicular to thefixed electrode surface such that the moveable electrode moves to thedesired position.
 11. The method of claim 10 wherein the moveableelectrode is a cantilever that includes a fixed end and a moveable tip.12. The method of claim 10 wherein the desired position is determined bythe height of the moveable tip.